The present invention is concerned with a controlled release dosage formulation that is based on the combination of a relatively hard, internal coated core material that contains the active medicament and a relatively soft, external phase that surrounds the internal phase and forms the external surface of the dosage formulation. The external phase comprises a water soluble polymer which may contain up to 10 wt % of water insoluble additives.
In order to provide a controlled release product, a water insoluble material such as a cellulose polymer or a wax has been used to coat discrete drug containing units such as drugs or crystals in order to resist the action of the fluids in the gastrointestinal tract. These coatings have resulted in the production of satisfactory pellets or granules that would usually be placed in a gelatin capsule because if a tablet was made by compressing the cellulose polymer or wax coated pellets, the coating would either rupture or become so deformed that the uniformity of any wax coating would be adversely affected.
The prior art has used microcrystalline cellulose to coat sustained release pellets (SR) pellets to provide cushioning and has used a major portion of cushioning agent to minimize the breakage of the SR pellets.